2.2.24 [HTML] Section 14.2.3, Header style information: the STYLE element


The specification states:

 type = content-type [CI]
 This attribute specifies the style sheet language of the element's contents and 
 overrides the default style sheet language. The style sheet language is specified 
 as a content type (e.g., "text/css"). Authors must supply a value for this 
 attribute; there is no default value for this attribute. 

All Document Modes (All Versions)

If the type attribute is not used it defaults to CSS and applies the style.